The present invention is directed to a method of and apparatus for continuous non-destructive testing of bar-shaped specimens formed having iron-containing material of specific quality characteristics. Individual specimens are moved at a definite translational velocity along an elongated path through a testing block which is coupled to an electronic testing installation for continuously comparing the specimens passing through the testing block via the electronic testing installation with calibrated artificial flaws of a defined magnitude previously stored in the testing installation. The specimens are classified based on the comparison afforded by the testing installation.
Bar-shaped specimens, particularly in the form of pipes or tubular members, are examined, during the course of a continuous passage, in accordance with preset standards in order to determine the presence or absence of flaws for assuring the quality characteristics described in an applicable specification. Mainly the testing processes used are based on magnetic induction or on acoustics. In both cases, a testing block is coupled to an electronic testing installation which has been calibrated with the help of a testing standard containing artificial flaws of a defined magnitude. When the testing standard is introduced into the testing block, the artificial flaws generate characteristic signals due to a change in the magnetic field (magnetic induction process) or by reflection (acoustic process). The amplitude level of the signals is arranged by suitable actuation links in the testing installation so that two response ranges are formed and assigned respectively to specific sorting compartments or trays in a sorting station. In the sorting station one sorting compartment receives accepted specimens while the other sorting compartment receives rejected specimens, that is specimens with a certain level of flaws.
The specimens, such as pipes, are located in a supply station which also serves as a material buffer, and are consecutively displaced from the supply station onto a roll table and conveyed therealong at a specific translational velocity through the testing block. Any specimen generating signals of an amplitude level in the testing block--electronic testing installation, equal to or larger than the amplitude level of the testing standard, are stored in the sorting compartment for defective specimens after they have passed through the testing block. Specimens causing no amplitude or amplitude levels lower than that of the testing standard, are stored in the sorting compartment for flaw-free specimens.
In actual practice, it has been found that the defective specimens contain a relatively high proportion of specimens which have signaled false or pseudo flaws during testing. As a result, the defective specimens are subjected to a repeat examination under the same testing conditions, for eliminating as many as possible pseudo flaws signaled during the initial testing operation. Pseudo flaws can occur due to external interference effects, such as controlled pulses, inductions triggered by control processes, uneven and/or erratic translation movement, off-centered guidance or by blows or shocks applied to the specimens. Such interference effects generate pulses in the electronic testing installation which are evaluated as flaw signals with the result that such specimens are identified as containing flaws.
The disadvantage in the known process and apparatus is that the repeat testing occurs at a time interval from the initial testing. Apart from the fact that each rejected specimen must be especially designated as such and subjected to further quality testing, with the requirement for appropriate conveying means and conveying tracks with buffer zones, the repeat testing has negative effects especially in interconnected manufacturing facilities located upstream and downstream of the testing devices, if the testing device is integrated into a cyclically flowing production line. In addition, in the known situation no precise interrelationship between the signals displayed by the electronic testing installation and the various flaw conditions in the specimens can be acquired. A subsequent machining for specific types of flaws in the specimen is essentially out of the question.